Synthesis of α-lithioarylmethanes of m-xylene and its α-trimethylsilyl derivatives; crystal structure of [{Li(Me₂NCH₂CH₂NMe₂)}₂{C₆H₄(CHSiMe₃)₂-m}]

Stereoselective Synthesis of meso-α,α‘-Bis(Chloromercurio)-α,α‘-bis(trimethylsilyl)-m-xylene

“…All commercially available starting materials were purchased from Aldrich Chemicals and used as provided. Compound 2 was synthesized according to the literature procedure …”

“…We recently reported the synthesis of α,α‘- m -xylenediylbis(mercurychloride) 5 ( 1 ) and decided to focus our attention on the preparation of some of its analogues. α,α‘-Bis(trimethylsilyl)- m -xylene can be easily lithiated at the benzylic postions to yield α,α‘-dilithio-α,α‘-bis(trimethylsilyl)- m -xylene ( 2 ) as a tetramethylethylenediamine (tmeda) adduct . In principle, the dimercuration of 2 could yield a racemic mixture of the optically active enantiomers ( rac form), the meso isomer, or a mixture of the rac and meso isomers.…”

“…R,R′-Bis(trimethylsilyl)-m-xylene can be easily lithiated at the benzylic postions to yield R,R′-dilithio-R,R′-bis-(trimethylsilyl)-m-xylene (2) as a tetramethylethylenediamine (tmeda) adduct. 6 In principle, the dimercuration of 2 could yield a racemic mixture of the optically active enantiomers (rac form), the meso isomer, or a mixture of the rac and meso isomers. In this paper we report that the mercuration of R,R′-dilithio-R,R′-bis-(trimethylsilyl)-m-xylene is highly stereoselective and yields solely meso-R,R′-bis(chloromercurio)-R,R′-bis(trimethylsilyl)-m-xylene.…”

Lithiation of 3,3‘-Dimethyl-2,2‘-bipyridine and Its Trimethylsilylated Compounds: X-ray Crystal Structure of [{2-CH(SiMe3)C5H3N}2{Li(tmeda)}2] (tmeda = N,N,N‘,N‘-Tetramethylethylenediamine)

“…−78 °C. The dilithium compound 1a was isolated as a dark red solid with low solubility in hydrocarbon solvent, presumably due to the formation of oligomers; [{Li(tmeda)} 2 {2-CH 2 C 5 H 3 N) 2 }] n , with structure similar to that of [{Li(tmeda)} 2 {2-CH 2 C 6 H 4 ) 2 }] ∞ , is a coiled polymeric chain with intermolecular bridging . Organolithium compounds tend to form aggregates, owing to the electron-deficient character of lithium, and the lithium−carbon bonds have a higher degree of ionic character …”

“…The lithium complex [LiCH 2 (C 6 H 5 )N(CH 2 CH 2 ) 3 N] n has been structurally characterized , These dilithium complexes have also been shown to be useful transfer reagents for the preparation of metallacycles. , It has been noted that monolithiation of xylene derivatives is dependent on the stoichiometry of Bu n Li and the choice of tertiary amine. , It was found that a more bulky tertiary amine such as pentamethyldiethylenetriamine (pmdeta) conducts monolithiation more effective than tmeda . In contrast, metalation of 2-methylpyridine and its trimethylsilylated derivative 2-CH 2 RC 5 H 4 N (R = H, or SiMe 3 ) with Bu n Li was found to be comparatively more facile even without the presence of tmeda, due to the fact that the free ligand 2-methylpyridine can act as a base ( via the pyridine nitrogen) to activate the lithium reagent in the reaction .…”